[Strain differences in the neuraminidase specificity of subtype N 1]

Nine strains having neuraminidase of subtype N1 and two strains in which the appurtenance of neuraminidase to subtype N1 was determined in the course of the study were examined for the antigenic specificity of the functional center of the enzyme in the cross neuraminidase activity inhibition test. Neuraminidase of the strains A/Swine/Tatarstan/64 and A/Swine/Ikshurminsk was shown to belong to the subtype N1 but to differ from neuraminidase of the strain A/Swine/Iowa/15/30. Neuraminidase of the strain A/Chicken/USSR/314/67 differs from neuraminidases of A/PR8/34, A/WS/33, and A/Swine/Iowa/15/30 but is related to neuraminidases of the strains A/New Jersey/8/76, A/duck/Germany/1868/68 and A/Chicken/Scotland/59. The A/New Jersey/8/76 neuraminidase is not related to neuraminidases of the strains A/PR8/34 and A/WS/33 but is related to neuraminidases of strains isolated from swine and domestic fowl. The disclosed considerable strain variations in the antigenic specificity of neuraminidases attest to heterogeneity of the subtype N1 and the possibility of its subdivision into groups.